1. Field of the Invention
The present invention relates to a communication system and more particularly to a arbitrary or chaotic waveform modem which includes an arbitrary waveform generator or modulator and a chaotic waveform demodulator configured as a sliding window correlator which includes non-uniform spaced tapped delay lines and a matched filter for modulating and demodulating chaotic as well as periodic waveforms to provide spectral efficiency heretofore unknown in communications systems.
2. Description of the Prior Art
Modems are well known in the art. Such modems are used to convert data signals to signals suitable for transmission. Such modems normally include a modulator for modulating outgoing data signals which are transmitted either by RF or optically to a demodulator which demodulates the incoming data signals. Both RF and optical modems are known. Optical communications systems are becoming increasingly more popular due to the ever increasing demand for higher data capacity and lower interference. Examples of such optical communication systems are disclosed in U.S. Pat. Nos. 4,084,182; 4,862,406; 4,866,699; 4,905,253; 5,311,344; 5,321,541; 5,675,674; 5,694,232; 5,703,708; and 5,742,423.
Both RF and optical communication systems are based on modulation of a periodic carrier signal, such as a sine wave. Unfortunately, the use of such periodic carrier signals limits performance and efficiency of the communication system. As such, there is a need for a more efficient and increased performance communication system.
The present invention relates to an improved communication system which provides improved spectral efficiency as well as relatively low co-channel interference modulation characteristics relative to known communication systems. In particular, the communication system includes a modem that includes an arbitrary or chaotic waveform generator or modulator and a chaotic waveform demodulator configured as a sliding window correlator that is adapted to modulate and demodulate arbitrary or chaotic waveforms. The modulator includes a finite impulse response (FIR) filter, for example, formed from tapped delay lines with unequal time delays. The demodulator is formed as a matched filter for recovery of the input data signals. The modem is adapted to transmit either optical or RF waveforms. In order to prevent drift of the tap weights due to temperature drift of the tapped delay lines and other factors, a closed servo loop may be provided for each tap weight. By maintaining the accuracy of the tap weights, the system in accordance with the present invention is adapted to provide arbitrary or chaotic modulation and demodulation of the input data signal thereby providing increased spectral efficiency and improved performance which provides increased data rates and quality relative to known communication systems based on modulation of periodic signals.